Hi all,
I had a circuit of output = -3V (for a lcd supply). However, when i connect the lcd up, the voltage to that pin drops to -0.7V. Initially I thought it may be due to the insufficient current, hence i changed the DC convertor in the circuit to a higher power. The voltage still drops to -0.7V.
Any reasons what caused the drop in voltage?
PS: the drop is actually increase. (-3.0 to -0.7)
Tks ywz
Replace the display with a variable resistor, momentarily, and see what resistance loads the supply to the same voltage. This will tell you about what the resistance of the supply is. Perhaps the LCD display has a short or near short in it.
-- Regards, John Popelish
I've seen things like this happen with poor ground connections. Check your grounds to be sure they're making good contact.
Hi,
Checked... all connected.
Erm, Sorry, but i don't quite understand this part.
The LCD is able to display black boxes when powered directly to a power supply.
I tried replacing the whole power circuit with a simple potential divider circuit. Again the voltage drops upon connection.
Vcc (8V) -- Connect to Vcc of LCD | >
< 5K resistor | O -- Connect to GND of LCD | > < 3K resistor | GND -- Connect to Vo (-ve voltage supply of LCD)Any ideas?
Tks ywz
Any ideas?
Is is a supply pin? Or perhaps a contrast pin?
In case of supply, maybe you missread, it should be +3V and you're running into some internal protection diode?
If it's contrast, maybe your LCD has contrast hardwired on the LCD board?
If none of the above, I don't know.
Goodluck!
What is the part number of the LCD you are using? Can you provide a link to the datasheet? Which pin numbers are you connecting power and ground to? In a later post, it looks like you are connecting a 5k resistor between Vcc and ground of LCD and a 3k between ground and Vo/-ve. However, it doesn't look like you have the ground pind of the LCD connected to ground (unless that is what the O is). That looks like it could be causing you some problems. What is supplying power and what is current capability?
Richard
yup the " O " is the connection to GND. This is to achieve the -3V.
In the original power supply circuit, I used a negative voltage op amp (TL084) to invert the 5V to -3V. The dc supply to provide the +- Vcc is by tying 2 dc convertor, 0.6A.
Another connection i tried for the negative voltage is:
Btw, the LCD is controlled using a PIC18F4331. The Vcc (5V) and Gnd of both circuits are tied together and connected to the LCD pins respectively. This is because the LCD only has a single gnd rail for its Vo, Vcc and Data lines.
Some background: The LCD is tested workable with the latter connection
ywz
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